Sunday, October 14, 2018

First HARA launch of 2018...

Warning! Many pics in this post!

Folks gathering around the RSO/LCO tents - Chris Short's trailer of wondrous rocket goodies is in the background
(Click to enlarge).
Yesterday's weather was perfect for flying rockets - mostly sunny skies, a light wind from the north, and afternoon temps in the mid-seventies. It was so nice and comfortable that I didn't even mind getting my aged carcass out of bed early to meet Allen for our 7:45 trip down to the new field. After a breakfast stop at Hardees, we arrived at the Butler Mill field near Woodville around 8:45. Chuck and Art were already in the process of setting up the range, which took till just past 10 AM. The first launch at a new location always starts out with a few issues and confusion - you have to figure out where to place the pads, work out where folks should park, etc. in addition to the normal launch set up. It'll go easier next time...

Looking towards the pads - I love this field! (Click to enlarge).
Art was instrumental in locating and getting permission for us to use the new field, so it was appropriate that his was the first rocket launched. Straight up into the blue, followed by a soft landing under parachute. Art's rocket set the pattern for the day - there would be many excellent flights, with not one drifting out of the field and only one - a model rocket - coming in ballistic.The launch pace was leisurely, with plenty of high power and model rockets taking to the air. I was surprised at the lack of mid power birds - we had some G flights, but I cannot think of a single F powered rocket that flew. Flyers started leaving the field around 3 - football is king in Alabama, and the games were summoning the faithful - so we closed up shop and left the field about 4. The 45 minute drive back to Huntsville went quickly, and I was uploading pictures to my computer by 5. Much better than the 2 hour trip back from the old field in Manchester!

Art's rocket under chute (Pic by Patrick; Click to enlarge).
The owner of the field is constructing an airfield on his property a little way from the corn field where we now fly. Soon after the launch began, we were started by the approach of two low flying airplanes, the second of which flew very, very low over the field just to the east of the range. So low that I was afraid it might crash when it banked away to the north east. Never before had this happened at a HARA launch, and we kept a close eye out throughout the rest of the day. I wonder if the pilots were a little wary of us, because scale models of AMRAAMs and Patriots were laid out on tables along the flight line, being quite popular with the attendees. The planes were so low they had to have seen them.

An airplane flies very low just east of the range (Pic by Patrick; Click to enlarge).
My list of some of the day's flights, in no particular order:

Allen flew his scratch-built scale cruise missile "Long Tom" on a K motor, achieving his NAR Level 2 certification. Congrats Allen!

Allen gets Long Tome ready for flight (Pic by Patrick; Click to enlarge).
Long Tom streaks skyward (Pic by Patrick;
Click to enlarge).
Long Tom under chute (Pic by Patrick;
Click to enlarge).
Elliot's high power Pike, Black Brant, and Darkstar Jr. rockets put in flawless flights. I was mostly interested in his modroc "fighter" collection - the Shrox fighter and the Odd'l Rockets F-104 did well, but the Odd'l Rockets F-16  had a recovery failure. Fortunately there was no significant damage after the dirt was cleaned out of the top of the body tube.

Elliot's Darkstar clears the rail (Click to enlarge).Elliot's fighter rockets at the RSO table
(Click to enlarge).
Patrick's 3D printed rockets - "Sign Here Please" and "Unclaimed Baggage" performed well, except that "Unclaimed Baggage" broke its nose cone when the main failed to deploy properly.

"Sign Here Please" and "Unclaimed Baggage" start their treks (Pics by Patrick; Click to enlarge).

As I said, there were a couple of AMRAAMs and Patriots on the field. The AMRAAMs were PML kits that flew on G and H white motors with apogee deployments - their owners got quite a bit of exercise. Jason flew his Patriot on a white, while Allen opted for an I212 smoky motor to power his model (he likes the dark plumes).

An AMRAAM takes to the sky on a G motor
(Click to enlarge).
Jason's Patriot rides a pillar of white fire
(Pic by Patrick; Click to enlarge).
A lightweight, minimum diameter 24 mm model made of carbon fiber that flew on an Aerotech E. This was a test flight before a mach busting attempt (using a G) to occur at Bama Blastoff in a couple of weeks.

2 flights of high impulse motors - Chris Short's "Gizmo" tore off the pad on an I599, whereas a small scratch built seemed to transport itself to 6000 feet on an H550 Super Thunder. I was surprised the latter held together, but it was obviously "built tough".

Michelle checks in at the RSO table (Click to enlarge).
Michelle's colorful scratch-built gets going
(Pic by Patrick; Click to enlarge).
The Oz rocket's motor ignites (Pic by Patrick;
Click to enlarge).
The Oz rocket deploys its parachute (Pic by Patrick; Click to enlarge).
Michelle and her dad launched a few scratch built modrocs and a mid power "tin man" themed Oz rocket on a G. Josh flew more model rockets than anyone - a Custom Ion Pulsar (which took a while to find among the harvested corn stalks), an Estes Air Show (one glider flew well, whereas the other tumbled to Earth), an OOP Estes 2127 Sizzler that came in ballistic when the rear-ejected pod broke away from the model, and repeated flights of a Comanche-3 in various configurations. The final flight was a D-C-C combo, which put the upper stage way, way up there. Fortunately, all stages were recovered, though the second stage required a bit of looking.

Josh hooks up his Ion Pulsar (Click to enlarge).
Josh's Estes Air Show on a C motor (Click to enlarge).Josh's Comanche-3 in motion (Pic by Patrick;
Click to enlarge).
Josh's Estes Sizzler leaves the rod powered by a Quest D16 motor (Click to enlarge).
I flew 4 rockets... First up was the Zoom Broom clone on an A3-4T. Good old Witch Hazel got her annual ride, ending with a comfy landing on the dirt. Next was the MPC X-2 Invader, featuring Marvin the Martian in its Looney Tunes decor. It was powered by a 1st gen Quest B4-4 Q-Jet, which required stripping off the motor label and a little effort to get it into the motor tube. Continuing the Halloween theme, my purple Target spider web candy bowl saucer made a short flight on an Estes C6-0. Finally,  a new Quest Q-jet C12-4 propelled my Big Bertha derivative, Beulah, containing a Jolly Logic Altimeter 3 to 427 feet. 

Witch Hazel rides her rocket (Click to enlarge).
Target candy bowl saucer on a C6-0 (Click to enlarge).The B4-4 Q-Jet in my MPC X-2 Invader leaves a trail
of black smoke (Click to enlarge).
Beulah descends under an orange parachute (Pic by Patrick; Click to enlarge).
Beulah's flight profile as recorded by the Jolly Logic Altimeter 3 (Click to enlarge).
That's this month's short summary... Can't wait for next month's launch!

Sunday, September 30, 2018

What I learned from this year's Geezer TARC...

I spent a lot of time with my designs and simulations this year. Here's what I took away from yesterday's launch:

Reliant's flight profile from the PNUT altimeter (Click to enlarge).
1) As expected, the simulated altitudes are overly optimistic, by tens of feet in my case. Reliant was predicted to go 874 feet; it actually flew to 801 feet, a difference of about 9%. In contrast, Artemis was simmed to 880 feet and flew to 871, a difference of only 9 feet. I'm thinking the latter is due to a set of fortunate circumstances, as the 9% is more in line with my expectations of a 10% difference in altitude. So if I was simming a TARC rocket, I'd select configurations that give altitudes about 70-100 feet above the goal (926 - 956 feet).

2) The online descent rate calculations did an excellent job predicting the descent rates - the choice of two 12" octagonal parachutes was perfect for egg capsules weighing close to 300 grams. I got measured rates of 22 and 23 feet per second, which are right on the money.

3) The BAMA Recovery Systems TARC parachutes took the stress, and they are octagonal, which increases the parachute drag. Plus they are lighter and cheaper than comparable Top Flight parachutes.

4) TARC teams using F32's in BT-70 rockets may be adding a fair amount of ballast this year to drop altitudes. Do lots of sims and choose your motors carefully based on the numbers. Watch the delay times - 6 seconds is close, 4 is way too short. Ejection should occur just past apogee, not before (as in the Reliant flight profile depicted above).

5) You can do this year's challenge on a cluster of 2 Estes E12-6's - Artemis' flight proved this. The question remains as to how consistent black powder clusters are from flight to flight. If you have to cluster, 2 motors are the easiest (naturally).

6) If you use the Perfectflite Firefly (cheaper, smaller, and lighter than the PNUT), get the field display unit. The flashing LED is tough to read on bright sunlit days.The Firefly is not a logging altimeter, but is kinda like the Jolly Logic Altimeter 2. Here's the data from Artemis' flight:
  • Apogee: 871 feet
  • Speed: 428 ft/sec
  • Time to Apogee: 7.4 sec
  • Flight Time: 44.6 sec
  • Descent rate: 23.4 ft/sec
  • FDD Battery: 3.06 V
  • FF Battery: 2.63 V
7) An "egg pusher" (BT-70 coupler bulkhead screwed to end of 18 inch 1/2" diameter wooden dowel) or something similar is a must if you are to get the eggs in/out without breaking them. 3 eggs are a pain to pack.

8) The Apogee egg cushions work well and are not that heavy. I flew the 2 egg cushion and a 1 egg cushion in each payload section.

9) Pack your parachutes very carefully - I used Estes wadding to keep the chutes separated in the body tube. You do not want the egg capsule parachutes tangling up - that would be bad.

That's what immediately comes to mind - hopefully some TARC teams find something useful in this post.

At long last...

In my previous post, I mentioned that the day was perfect for flying - clear skies, light wind, and comfortable temperatures. Soon after arriving at Pegasus, I realized that the latter was most definitely not true; low-to-mid eighties may seem not so bad when displayed on the screen of a cell phone, but experiencing them in the middle of a field puts quite a different perspective on the definition of hot. By the time the launch ended at 2 or so, I was panting like a rabbit after being chased by hounds. Sun block and water, my friends - bring them, use the former and drink the latter. They are your tickets to making it through a hot launch day.

Anyway, on to the launch...

Duane and I arrived at Pegasus about 11; folks were already there, including Fletcher Cannon, a new Geezer TARC participant, and Marc Loertscher, who won the contest a couple of years back. Marc was there to watch this year, and had brought along a young one to observe the anticipated carnage. Duane, Fletcher, Allen, and I proceeded to set up the range, and the other contestants - Patrick and Vince - showed up as we were putting things in place. All was ready to go around 11:30, by which time we had a nice crowd of family, local TARC team members, and UAH students settling in for the show. It was time to get some rockets airborne.

Allen's Cosmic Explorer starts the launch
(Click to enlarge).
Duane's Cherokee-D puts in yet another flight
(Click to enlarge).

Allen's modified Partizon on a CTI G83
(Click to enlarge).
Art Woodling's scratch leaves the pad on a D12-5
(Click to enlarge).
Allen started things off with his Estes Cosmic Explorer, which barely topped 300 feet riding an obviously defective F30 motor. A C6-7 put Duane's venerable Cherokee-D way up there, providing a good check on the wind direction despite a parachute failure; the rocket landed horizontally on the weeds, undamaged. Allen's modified Estes Partizon was up next on a CTI G83 Blue Streak reload. It reached an altitude of 1138 feet, and the dual deploy worked well, even though Allen forgot to reset the main deploy altitude to something appropriate for Huntsville (He last flew it at NARAM in Pueblo). Art was the last to fly before the Geezer TARC flights began. His scratch-built 24 mm powered rocket - the 1st rocket he flew with HARA - put in a flawless performance on a D12-5.

And now for the Geezer TARC flights...

Patrick with his 3D printed "Geezer III" (click to enlarge).
Patrick courageously went first, but his 3D printed orange Geezer III rocket had an igniter misfire. A new igniter was put into place, but the F22J reload seemed to have trouble getting going - it huffed a bit before coming to power, and the rocket only reached 488 feet altitude, far below the 856 foot goal. After the launch, I noticed that the picture sequence of the launch showed the igniter wires (and presumably the igniter) hanging on until the rocket had almost cleared the rail - that didn't help the performance. The good news is that the 3D printed model showed no signs of melting - which even Patrick expected - so Geezer III can fly again.

Sequence showing Geezer III dragging the launch cables with it (Click to enlarge).

Fletcher stepped up next, and his Saturn-decor rocket put in a very good flight. It soared to 906 feet and was down in just over 53 seconds - a solid 79 score, good enough to make me sweat even more in the midday heat.

The purple exhaust of the Blue Thunder motor in
Fletcher's rocket (Click to enlarge).
Fletcher's rocket clears the rail (Click to enlarge).
My turn had come - I placed the Reliant on the pad, hooked up the clips, and asked Duane to do the count and launch while I took pictures with my phone. All those hours of simulations and fretting over parachute sizing had come down to this moment, and I could only hope that my shaking hand would not mess up the launch pictures. Reliant, powered by an Aerotech F30FJ-6, rode a pillar of black smoke into the sky, its path straight and true, with no spin. Ejection occurred just past apogee, and I was relieved to see all three parachutes - two on the egg capsule and one on the sustainer - fully deploy. The egg capsule landed just a little over 41 seconds after launch, with the sustainer touching down about 20 seconds later. I was elated to hear the PNUT altimeter beep out a peak altitude of 801 feet, and even more excited when the eggs were confirmed to be without cracks. For the first time in Geezer TARC, I was in the lead, with a 62 score. Only Duane and Vince stood between me and victory, and even if one of them bettered Reliant's score, I still had my second entry, Artemis, waiting in the bullpen.

Reliant's F30FJ leaves a trail of thick black smoke (Click to enlarge).
Duane placed his entry on the pad. Painted blue with a gold nose, this rocket was a little smaller than mine, and had a finish a bit on the rough side, which he hoped would cause enough drag to offset the power of the loaded Aerotech F32-6T. His hopes were quickly dashed, as the rocket bulleted off the pad, almost disappearing in the blue of the sky. Clearly too high, but the amazing thing was that the egg capsule landed almost exactly 45 seconds after liftoff - a perfect time. Sure enough, the altimeter reported 1102 feet (the highest TARC flight of the day), so we were left scratching our heads as to how those eggs got down under two deployed 14" parachutes from that altitude in just 45 seconds total. At the needed descent rate of about 23 feet per second, it should have taken something like 55 seconds. I hope Duane will share his altimeter data, because inquiring minds want to know. Last year, Duane's flights were too low; this year's was too high, giving him a 254 score.

I was still in the lead, but the reigning TARC Geezer, Vince, the creator of Frankenstein rockets and shunner of simulations, was next. Would he neutralize all my scientific and engineering efforts with a thrown-together model and a randomly chosen motor from his stash? He had carefully kept his entry in his vehicle until this moment, and I was quite apprehensive as he approached the pad with this year's creation. The time of reckoning had arrived...

Vince's model surprised me by being a fairly conventional egg lofter. Painted white, with red fins, an orange transition, and a yellow nose, the rocket's egg capsule consisted of a length of ST-20 tube and the transition and nose cone from an old Estes Scrambler (the 1980's version) or Omelet Express.  The sustainer was based on Estes BT-60 tubing, with a 24 mm motor mount and swept fins. I had considered something similar back when the rules were announced in May, but abandoned the concept because of the limitations imposed by the BT-60 lower section. The lower weight and surface area (less drag) put this model in the twilight zone of motor choices - E's were not enough power, and F's were too much. You can only cluster up to 3 18 mm motors in a BT-60, and 3 C6's were not going to get the job done. So this design was not viable unless I was willing to cluster composites (3 AeroTech or Quest D's), and I am not yet crazy enough to try that with a trophy on the line.

Vince's rocket rides white fire up into the puffy clouds (Click to enlarge).
Vince's flight made me glad I tossed the design. His rocket was way, way overpowered on an Aerotech F44-8W, achieving a peak altitude of 1009 feet and a duration of 107 seconds. A 399 score, which meant I was the winner of Geezer TARC!

Vince holds this year's Skunk trophy (Click to enlarge).
Finally! I got the victor's trophy, and Vince, last year's winner, got the the Skunk trophy for the worst flight. After all, 1) his score was bad, and 2) his rocket was the only one to sustain damage, when the streamer on the sustainer failed to deploy. Cracked a couple of fins.

I was sorely tempted not to fly Artemis - I had won, it was hot, and I wanted some food - but the old girl beckoned to me from the car. So I loaded her up with eggs and a Firefly altimeter, and stuck 2 Estes E12-6's into the motor mount. I figured that these would provide enough power to get me close; 2 additional A or B motors would be risky, as simultaneously lighting 4 motors is no picnic. She quickly left the pad on a straight-up trajectory, with chutes deploying just past apogee. The egg capsule landed just over 45 seconds after liftoff - a perfect time - with the sustainer landing near the southwest corner of the field quite a bit later (24" parachute was too large). The Firefly display showed a peak altitude of 871 feet, just 15 feet too high. A 15 score - the best ever in Geezer TARC, and good enough for a qual attempt. I am very glad I flew Artemis!

The plumes from the dual E12's are visible as Artemis leaves the pad (Click to enlarge).
2018-2019 Geezer TARC scores (Click to enlarge).
Duane's Mammoth on an F52 (Click to enlarge).Josh's Nike-X powered by a C6-7 (Click to enlarge).

The launch lurched to an end soon after Artemis' flight - Duane flew his Mammoth on a F52, and there were a few model rocket flights. Around 2 we packed up and left the field. Upon arriving home, I placed my trophy on my rocket shelf, where it sits proudly. I am very pleased - to quote Mark Watney, "I scienced the sh*t out of this."

And it paid off.


Saturday, September 29, 2018

The hours before...

Today is clear and comfortable, with light winds out of the NNE - perfect for the Geezer TARC launch in a few hours...

Ready to compete!

I'm all packed up, with altimeters charged, eggs weighed, rockets loaded with parachutes, and low power pad/controller bagged for use by the modroc flyers. So why did I fret last night, and why I am still fretting?

Because I have doubts about the parachute sizes I have chosen for the payload section, that's why! I woke up in the middle of the night and revisited my descent rate calculations using three different utilities - 2 online, and the app on my iPhone. And I'm still reviewing them this morning, wrestling with the basic issue, which is that all the numbers indicate my chosen 12" parachute size is marginal for the challenge, producing a descent rate of around 23 feet per second. A tad too fast, but the next commercially available size - 15" - would definitely keep the eggs up there way too long. I am wishing I had the talent/ability/motivation/etc. to make my own rip stop nylon parachutes, because I sure could use a couple of 13" diameter hexagons right now. Alas, it's too late, and I'm going to have to make do with what I've got.

Top Flight parachute compared to that from BAMA (hexagon vs. octagon)

To show you how nervous I am, I opted to use some new parachutes I ordered from BAMA Recovery Systems instead of my tried and true Top Flight brand. The BAMA chutes are octagonal in shape, with 8 long shroud lines instead of 6 - this supposedly increases the parachute drag coefficient, slowing the descent. I'm a) hoping this is the case and b) they can take the stresses that are going to happen with that egg capsule is ejected from the sustainer. It'll be very sad and messy if those shroud lines break.

I'm also second-guessing my motor choices, but that's normal before a Geezer TARC launch. We'll see how things go on the field.

Stay tuned...

Friday, August 31, 2018

Another Boy Scout rocket...

I just finished the Estes "Space Exploration" Boy Scout rocket, which I bought in a bulk pack from the Boy Scout store (Scout Shop) many moons ago. It was a great deal - 6 rockets for $30, including shipping; unfortunately, this product has been discontinued, with the only offerings being standard Estes fare. The reason is pretty clear - Estes has stopped producing the Ricochet, and the Space Exploration rocket was nothing more than a Ricochet with different stickers. So it went bye-bye with the Ricochet.

The kit parts are good Estes quality - laser-cut fins, nicely fitting plastic adapter and nose cone, and decently strong body tubes. I would rate this build a definite skill level 2, as you have to line up the three components making up the fin. This is more tedious than hard, but it does require that you pay some attention to what you are doing. Finishing was straight forward - 4 coats of Brodak sanding sealer on the fins, then a couple of coats of primer followed by the paint. I screwed up the paint scheme by relying on my failing memory, for if I had bothered to take another look at the box art, I would have seen that one fin was red and the others blue. My memory had all four fins blue, and that's how she was painted. The stickers went on easily, but appear shiny against the paint - you can tell there are stickers on the model. Why can't Estes just give us waterslide decals, which look so much better? I know - stickers are easier for young ones to handle, but they all too often look crappy to us old geezers.

Boy Scout "Space Exploration" rocket (Click to enlarge).
Anyway, the rocket turned out OK, as you can tell from the pic. A bit of trivia for you non-Scouts - the circular logo beneath the American flag is a replica of the Boy Scout Space Exploration merit badge. I thought it was kinda neat that they managed to incorporate that into the kit.

Now it's back to assembly line - I have to apply the second primer coat to the lower part of the Artemis (my 2nd Geezer TARC rocket), build an egglofter for the NRC Eggloft Duration event, and finish assembling my Apogee tower. Gonna be a busy weekend...

Sunday, August 26, 2018

Time to do some TARC math!

Now that the Reliant is finished, it's time to figure out the size of the parachutes needed to land the booster and payload sections safely. To do so, you need to measure the weights of both these sections, which in my case are 178 and 318 grams, respectively. The booster is easy, as one can choose the descent rate and size the parachute accordingly. A "safe" descent rate - one that avoids damage to the fins - is usually around 15 feet per second, so we go to one of several handy-dandy parachute descent rate calculators available on the Internet - I use either Model Rocket Parachute Descent Rate Calculator or Descent Rate Calculator - Rocket Reviews or an app I have on my iPhone. All 3 give similar results, so the choice does not really matter.

But, wait... Why can't we just use Open Rocket, as that's the design program? It gives descent rates, doesn't it?

Yes, but Open Rocket cannot handle the case where the payload section comes down separately from the other section. So what it will give you is a descent rate based on the sum of the areas of all your parachutes and the total weight of the rocket. That's not going to work this year. So we are going to have to do things outside of the simulator. If you use Rocksim, you can trick it into handling this year's TARC circumstances by creating a 2 stage rocket and designating the payload section as a motorless upper stage; you can then attach a recovery device to each stage and set the deployment circumstances. However, most folks don't have Rocksim.

Now I'm ready to do the compute the booster chute size, so I bring up the RocketReviews calculator and put in the booster weight. I prefer to use Top Flight thin mil rip stop nylon parachutes, which are hexagonal in shape, so I choose "hexagonal" from the Parachute Shape drop down menu. Just for grins, I put in the altitude goal of 856 feet, and finally make a guess at the right parachute size before I click the "Submit" button:

Click to enlarge.
It appears that my initial guess of 15 inches was too small - the calculator is recommending a parachute size of 18 inches. Recalculating with this value yields

Click to enlarge.
This is pretty close to my desired descent rate of 15 feet per second, so I'll run with it. My booster parachute will be an 18" Top Flight, bright orange in color.

Now for the harder part - the two identically-sized parachutes attached to the payload section carrying the eggs and altimeter. To calculate this, we must first figure out the required descent rate to land the payload section 43 to 46 seconds after liftoff, which means we have to go to our simulations to get the time of ejection, and subtract that from the duration goal to get the length of time the parachute is deployed. Open Rocket tells me that it will take about 7 seconds to reach 856 feet, so I will subtract that value from the midpoint of the duration goal - 44.5 seconds - to get the parachute time. The descent rate - in feet per second - is simply the altitude (856 feet) divided by the parachute time (37.5 seconds), or
So we need 2 parachutes that will lower the payload section at 22.8 feet per second. Now I go back to the descent rate calculator and put in the weight of the payload section, keeping everything else the same:

Click to enlarge.
Turns out that 18" is pretty close, with a descent rate of 22.6 feet per second. If I fiddle a bit, I end up with a parachute size of 17.8".

However, I need two parachutes, not one, so how do I do that? What I need to do is divide the area of the above by 2 to get the area of each identical chute. Since area goes as the square of the diameter, this means I must divide the diameter by the square root of 2 to get the size of my chutes. Doing so gives me a diameter of 12.6". I can check my work by doing a comparison:
which is close enough for government work.

Trouble is, there are no 12.6" commercially available rip stop nylon parachutes. The closest match is the 12" diameter. So what happens if I use that? Well, 2 12" parachutes have a scaled area (I'm leaving out the factor of pi) of 288, which translates to a diameter of square root of 288, or 17.0". I can now plug this value in into the descent rate calculator, which gives:

Click to enlarge.
This shaves about 1 second off the time, but it is still within the allowed duration range. Quite acceptable, especially given that I really don't want to have to learn to make nylon parachutes. Therefore, Reliant's booster will be recovered by an 18" parachute and the payload section will be brought down by two 12" chutes.

This concludes today's TARC exercise.